Method and circuit for detecting a fault of semiconductor circuit elements and use thereof in electronic regulators of braking force and of dynamics movement of vehicles

ABSTRACT

A circuit for detecting a defect of electronic components in an electronic control unit includes an output for driving a load ( 3 ). A redundant measurement of the current (I L ) is executed at the contacts (G, S, D), in particular at the driven contacts (S, D), of one or more semiconductor circuit elements, and an error function of a semiconductor circuit element is detected when the comparison of two current values (I S , I Sense1 , I Sense2 ) by way of the current flowing through a load ( 3, 3 ′) indicates an unequal current distribution. This circuit is of use in electronic brake force or driving dynamics controllers for motor vehicles.

BACKGROUND OF THE INVENTION

[0001] The present invention relates to a method of detecting a defectof semiconductor circuit elements, in particular of field effectsemiconductor circuit elements, a circuit configuration, and anelectronic controller with such a circuit configuration.

[0002] Electronic control devices for motor vehicle brake systemsperform functions at an increasing rate that either contribute todriving safety or lately even comprise basic vehicle functions such asthe braking function itself. Examples of functions for improving drivingsafety are anti-lock control (ABS) or driving dynamics control (ESP:Electronic Stability Program). The braking function as such is carriedout by the electronic control unit of the brake in more recentelectronic brake systems, such as the ElectroHydraulic Brake (EHB) orthe ElectroMechanical Brake (EMB). Therefore, ever increasing demandsare placed on the reliability, failure tolerance and error handling ofthe electronic control units.

[0003] It is known in prior art to install safety devices in electroniccontrol units for motor vehicle brake systems, which permit detectingany occurring defects of the electronic components contained in thecontrol units. Upon detection of such a defect, appropriatecountermeasures such as the deactivation of the control unit orswitch-over of the control unit into an emergency mode may be taken.Safety-relevant circuit parts may have a double or multiple (redundant)design to identify defects. Errors arising can be detected in many casesby comparing the functioning of the multiply provided circuit parts.

[0004] Semiconductor circuit elements such as power field effecttransistors (power MOSFET's, FET's) are employed among others foractuating the electromechanical hydraulic valves provided to control thebrake pressure.

SUMMARY OF THE INVENTION

[0005] The method of the invention being implemented in an electroniccontrol unit, in particular for brake or driving dynamics controllers,permits detecting a fault of electronic components, such as FET's, whichare associated with at least one power driver stage and at least onerecirculation driver stage. The power driver stage and the recirculationdriver stage preferably comprise electronic components such as,especially, one or more semiconductor circuit elements and/or one ormore current measuring devices.

[0006] Preferably, one power driver stage is respectively connected to aload, said load especially being an inductive load, e.g. a valve coil.

[0007] It is preferred to use sense semiconductor circuit elements assemiconductor circuit elements for measuring the current. These sensesemiconductor circuit elements are preferably Sense FET's.

[0008] Redundant current measurement relates to the testing of thecurrent in a redundant circuit arrangement with at least two currentmeasuring devices, and said current measuring devices can be arranged inparallel or in series to one another.

[0009] Apart from a measurement of the current at the output of asemiconductor circuit element, for example, the measurement of thedrain-source current in a FET, it can also be expedient for monitoringthe proper functioning of this semiconductor to determine the currentbetween the control line of the semiconductor circuit element and one ofthe outputs, e.g. the gate-source current.

[0010] Beside the multiple design of individual components for thepurpose of redundant current measurement, it can be expedient inaddition to use at least two semiconductor circuit elements that drivethe same output in order to increase the safety in operation. It is thenpossible to perform an individual current measurement especially on eachof these elements. Preferably, the control line of the semiconductorcircuit elements is driven jointly by one signal input with thesesemiconductor circuit elements that drive a common output. When one ormore of these semiconductor circuit elements drive induction currents ofinductive loads connected to the output, this also signifies anactuation of one output with several semiconductor circuit elements.

[0011] When a fault of a component is detected according to the methodof the invention, it is preferred to take one or more of the measuresout of the group—activation of a spare component for the semiconductorelement that failed, disabling of the brake control system,—activationof a partial operation or—display of an error signal on the instrumentpanel.

[0012] The invention also relates to a circuit comprising one or moresemiconductor circuit elements each with control contacts for connectinga control line, with current contacts for connecting preferablyinductive loads (e.g. valve coils) and a current measuring device fordetermining the current (I_(L) or I_(LS)) conducted through thesemiconductor circuit element, in particular for implementing the methodof the invention as described hereinabove, wherein at least two separatecurrent measuring devices are provided, optionally with one or morejoint components (R_(s)*), in particular, elements of a resistor, for aredundant current measurement.

[0013] Favorably, current measurement is determined by measuring thevoltage drop across resistor elements. When integrated on a substrate,resistor elements can be on-chip resistors or, preferably, discreteresistor elements, and it is possible to manufacture the last mentionedresistor elements with lower tolerances compared to on-chip resistors.

[0014] The invention also relates to electronic brake force or drivingdynamics controllers for motor vehicles which include a circuit asdescribed above.

[0015] Preferred embodiments of the invention can be taken from the subclaims and the subsequent description of the Figures comprising severalembodiments according to the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In the drawings,

[0017]FIG. 1 is a circuit with a Sense FET for driving a load, equippedwith a current measuring device.

[0018]FIG. 2 is a circuit for driving a load with a redundant currentmeasuring device.

[0019]FIG. 3 is a circuit with parallel connected Sense FET's withrespectively one current measuring device.

[0020]FIG. 4 is a circuit for driving several loads, equipped withcurrent measuring devices and an external reference resistor.

[0021]FIG. 5 is a circuit with a recirculation driver.

[0022]FIG. 6 is a diagram with current and signal courses of the circuitfor explaining the circuit according to FIG. 5.

DETAILED DESCRIPTION OF THE DRAWINGS

[0023] In the circuit according to FIG. 1, a Sense FET 1 is connected toterminal 15 leading to a load 3 (e.g. valve coil). A current IL flowsthrough load 3 according to the gate voltage at gate G. The secondconnection of the load (terminal 26) is connected to the positivepotential V_(REF) with a voltage relative to the reference potentialV_(REF). The additional sense output of a Sense FET 1 in which theconsiderably lower sense current I_(S) flows can be used to measure theoutput current. To convert the current into a voltage signal U_(S), thesense output is conducted through resistor R_(S) to the referencepotential.

[0024] The mode of operation of a Sense FET can e.g. be seen in U.S.Pat. No. 5,079,456 or patent application DE 195 20 735 A1. Accordingly,the load current of a power FET 18 can be sensed in that connected inparallel and in direct vicinity to the power FET 18 on the semiconductormaterial is a similar FET 8 having a smaller surface. Current I_(s) thatflows through the smaller FET is largely proportional to the loadcurrent of the power FET, however, current I_(s) is lower than the loadcurrent by a structurally defined numerical ratio, correspondingsubstantially to the ratio of chip surface used between power FET andSense FET.

[0025] A Sense FET is illustrated in FIG. 2, which comprises tworedundant Sense FET regions 8 in contrast to the Sense FET in FIG. 1.Both Sense FET regions are respectively carried through an own measuringresistor 4 (R_(s)) to the reference potential so that redundant currentmeasurement can be performed. The voltage U_(s) that is proportional tothe load current can be tapped between terminals 5 and 6 and betweenterminals 27 and 6.

[0026] However, in contrast to the circuit according to FIG. 5, thecircuit illustrated herein is limited to the detection of errors of themeasuring resistor 4 or faults of the Sense FET, which also extend tothe Sense FET region of the semiconductor, i.e. in the event of completemelt of the component.

[0027] The circuit in FIG. 3, wherein all essential components aregrouped on a semiconductor substrate 9, comprises two parallel connectedSense FET's 1 and 1′ for driving a load 3. The dotted frame 17emphasizes that Sense FET's 1 and 1′ can be seen as a common driverstage.

[0028] Besides circuit elements 1 and 1′, substrate 9 comprises twocurrent measuring devices 7 made up of reference resistors 4 and signalamplifiers 7 allowing the measurement of the respective voltages thatdrop across resistors 4. The measured voltages can then be carriedthrough outputs ADC1 and ADC2 to one or more A/D converters 38. Terminal15 of the circuit is connected as a low-side actuator to load 3.Terminal 15 leads on the substrate to the drain zones D of the SenseFET's 1 and 1′. Gates G of the Sense FET's are led jointly throughcontrol lines 16 to terminal 19, through which a control signal can besupplied by a logic (not shown). Discrete resistor elements R_(S), R_(S)are respectively coupled to the Sense FET regions of the circuitelements 1 and 1′ for generating a voltage proportional to the current.The voltage declining across resistors Rs can finally be tapped by meansof amplifier stages 7.

[0029] Sense FET's 1 and 1′ in FIG. 3 are favorably not arrangeddirectly side by side on the semiconductor substrate so that a defect ofone semiconductor element and the local heat developing due to saiddefect will not cause any defect of the other semiconductor element.

[0030] The circuit in FIG. 4 shows an embodiment with several drivers 24for driving respectively one of the loads 3, 3′ associated with thedriver. Herein, like in FIG. 3, the loads are driven by means of SenseFET's, however, herein a presentation of the Sense FET's 1 and 1′ isused which is broken down and differs from FIG. 3 for reasons ofclarity, as will be explained hereinbelow. In FIG. 4, the sense currentsection 8 of the Sense FET 1 is illustrated as an independent FETsymbol. The load current section 18 of the power FET 1 is alsocharacterized as a separate FET symbol.

[0031] In contrast to FIG. 3, current measurement is executed by usingan external discrete measuring resistor 4 allowing to connect the sensesections 8 of the n-fold provided (n>1) Sense FET's 1, 1′ to terminal 10(Select) by way of a signal in a selectable manner. To select the SenseFET region, gate 20 of the power FET 18 is coupled to gate 21 of thesense current section 8 of the Sense FET 1 by way of an additional FET12 (pass transistor). Further, there is a connection between gate 20 anda driving port 22 (Drive1). The gate of FET 12 leads to selecting port10 (Select1) and through inverter 11 to the gate of FET 13. Thesource-port of FET 13 is connected to the reference potential. Thedrain-port of FET 13 is coupled to the gate of the sense current section8. The drain-ports of the load current section 18 and of the sensecurrent section 8 are jointly conducted to terminal 15. Source-port 23is connected to reference resistor 4 by way of terminal 28. Terminal 28leads to amplifier 7 providing a signal at output ADC of the circuitthat can be processed further. The signal at output ADC is thenproportional to the respectively selected coil current in the event ofproper functioning of the circuit. Terminal ADC is connected to an A/Dconverter that provides a digital signal to a digital monitoring circuit39 having select outputs by means of which the Sense FET's in the driverstages can be selected.

[0032] In the operation of the circuit of FIG. 4, the signal carriedthrough output ADC indicates the current by means of that coil that isselected by a high-level at terminal 10, while a low-level must beapplied at that time to the other terminals of the remaining assemblies24. The selection of the driver stage 40 by means of a ‘high’-level atterminal 10 causes opening of FET 13 and closing of FET 12. Thisactivates the sense current section of FET 1 so that sense current Isflows through resistor 4. With a ‘low’-level at terminal 10, the sensecurrent section 8 will be deactivated so that current measurement can beexecuted by a ‘high’-level at terminal 10 at one of the remainingassemblies 22.

[0033] As illustrated in FIG. 3, the Sense FET 1 in one single driverstage can also be replaced by two parallel connected Sense FET's 1 and1′ corresponding to the embodiment in FIG. 3 or by a ‘series connection’like in FIG. 5 for the purpose of enhancing the redundancy. The resistorelements 4 can also be designed redundantly in the way of severaldiscrete components arranged outside the substrate.

[0034] When an unequal current distribution, as illustrated in FIG. 3,is detected by means of the method of the invention by comparison of thecurrents measured at the Sense FET's 1 and 1′ in the monitoring device39, an error signal is outputted at terminal F (FIG. 4).

[0035]FIG. 5 schematically indicates a circuit for driving an inductiveload 3, wherein besides a driver stage 25 for driving the load 3, thereis additional provision of a recirculation driver stage 29.

[0036] The circuit described herein is advantageous in comparison to thecircuit of FIG. 3 because faults of the power section in the Sense FETcan additionally be detected, which e.g. have a gradual or abrupt changein the switching resistance R_(DSon) as a result. In addition, a faultin the Sense FET of the recirculation stage can be detected accordingly.

[0037] The mode of operation of the circuit is explained by way of FIG.6. By driving the driver stage 25 by means of a square-wave signal 33 atterminal 19, the induction current I_(L) (freewheeling current)prevailing in the pulse pause due to the coil inductance can be fed backinto the coil by way of the recirculation stage 29. To this end, therecirculation stage 29 is driven by a signal 34 that is complementary tosignal 33 at terminal 30.

[0038] Driver stage 25 and recirculation stage 29 may expedientlycomprise one or more FET's.

[0039] Driving the driver 25 can take place corresponding to the circuitdescribed hereinabove in Fiqure 3 by way of a logic through terminal 19,which is connected to the driving line of a semiconductor circuitelement. A signal complementary to the signal applied to terminal 19 issent through terminal 30.

[0040] It is essential that both driver stage 25 and recirculation stage29 comprise each one of the previously described current measuringdevices (e.g. one Sense FET in each stage). When the coil is drivenaccording to the principle of pulse width modulation (PWM), this allowsredundantly determining the current that flows through the coil.Compared to the parallel arrangement of the Sense FET according to FIG.3, the circuit includes the advantage that semiconductor defects canadditionally be detected, where a change of the switching resistanceR_(DSon) occurs. Under the assumption that a corresponding defecthappens only in one of the existing semiconductor circuit elements(simple fault), a defect can be detected by a comparison of the currentthrough the driver stage during the driving phase with the freewheelingcurrent through the recirculation stage during the driving pause.

[0041] Current can be measured corresponding to FIG. 3 by tapping thevoltages at the measuring resistors 4, and the tapped voltage signalscan be amplified by amplification stages 7 also herein and relayed toone or more analog-digital converters 38 through outputs ADC1 and ADC2.

[0042] The circuit described hereinabove allows detecting deviationsbetween driving current and freewheeling current. Deviations can developwhen the measured current in the driver stage or in the recirculationstage does not coincide with the actual coil current. In this case, adefect of one of the Sense FET's is likely, what causes e.g.deactivation of the anti-lock system. The circuit according to FIG. 5renders it possible to detect apart from semiconductor defects alsoshunts, represented by resistors 31 (R_(p2)) and 32 (R_(p1)), whichoccur due to a defect either in parallel to the driver stage or inparallel to the recirculation stage.

[0043] In the event of a shunt corresponding to a resistor 32, thecurrent I_(Sense1)≈I_(LS)=I_(L)+I_(Leak1) is measured by Sense FET 25,wherein I_(L) is the current through coil 3 and I_(Leak1) is the leakagecurrent through resistor 32. The result due to the parallel connectionR_(DSon) and R_(P1) is that I_(Sense1) also comprises the currentI_(Leak1). Assuming that a voltage of e.g. 1 volt maximally can dropacross driver 25, I_(Leak1)<1 V/R_(p1) will result. Assuming that avoltage of maximally about 1 volt can also drop across the recirculationstage, a recirculation current I_(sense2)≈I_(Recirc)=I_(L)−I_(Leak1),with I_(Leak1)<(V_(REFx)+1 V)/R_(p1) will be produced after thedeactivation of FET 25. This shows that, with a positive leakage currentI_(Leak1) across resistor 32 with a shunt of the driver 25, the drivercurrent determined by the Sense FET is increased and the measuredrecirculation current I_(Recirc) in Sense-FET 29 is decreased so that adifference in current between I_(sense1) and I_(sense2) is produced,which can be detected by the circuit.

[0044] In the case of a shunt in parallel to the recirculation stage,symbolized by resistor 31 (R_(p2)), a higher currentI_(LS)=I_(L)+I_(Leak2) is required during the driving phase than thiswould be the case without a shunt. In this case, too, the relationI_(Leak2)>(V_(REF)−1 V)/R_(p2) applies in a maximum voltage drop of 1volt at the driver stages. During the coasting phase, when the coilcurrent discharges through step 29, a currentI_(Sense2)≈I_(L)=I_(Recirc)−I_(Leak2), with I_(Recirc)>−1 V/R_(p2), ismeasured in the Sense FET of this stage. A too low current I_(sense2) ismeasured by the parallel connection of the switch-on resistor R_(DSon)in the transistor of the recirculation driver and the resistor R_(p2).Consequently, the result is a current difference between I_(sense1) andI_(sense2), which can be detected by the circuit.

[0045] The method described in the preceding paragraph permits detectingshunts, under the precondition that resistor 32 is greater than zero.Fault detection by way of the current difference I_(sense1) andI_(sense2) alone is not possible in the case of short-circuit inparallel to the driver stage 25 or of the Sense FET itself. Therefore,it is preferred that a monitoring circuit with a comparator 35 isadditionally provided in the circuit according to FIG. 5, whichcomparator monitors terminal 15′ (coil output) as to whether the voltagepotential falls below a predetermined value. Even this case of faultwhich has not been identifiable so far, can be detected by the circuitby additionally monitoring the signal at terminal 36 alternating from‘high’ to ‘low’ when the mentioned short-circuit occurs.

1. Method of detecting a defect of electronic components in anelectronic control unit with one or more outputs (15, 15′) for thedriving of loads (3, 3′), characterized in that redundant measurement ofthe current (IL) flowing through the semiconductor circuit element isexecuted at the contacts (G,S,D), in particular at the driven contacts(S,D), of one or more semiconductor circuit elements, and an errorfunction of a semiconductor circuit element is detected when thecomparison of two current values (I_(S), I_(Sense1), I_(Sense2)) by wayof the current flowing through a load (3, 3′) indicates an unequalcurrent distribution.
 2. Method as claimed in claim 1, characterized inthat the gate potential and/or the drain potential (37) of semiconductorcircuit elements is determined by comparison with a nominal potential,and a circuit defect is considered to prevail when a deviation isdetected.
 3. Circuit comprising one or more semiconductor circuitelements (1, 1′, 1″, 25, 29) with control contacts (G) for connecting acontrol line (2, 16), with current contacts (S, D) for connecting one ormore loads (3, 3′ and at least one current measuring device (4, 5, 6, 7,8) for determining the current (Is) conducted through the semiconductorcircuit element, in particular for implementing the method as claimed inclaim 1 or 2, characterized in that the current (I_(L)) led to a load(3, 3′) and the current (I_(Recirc)) fed back from this load into thecircuit is determined by at least two current measuring devicesassociated with the same load, and a comparison device (38, 39) isprovided which compares the currents measured by the current measuringdevices.
 4. Circuit as claimed in claim 3, characterized in that thecurrent measuring devices comprise Sense semiconductor circuit elements(1, 1′, 25, 29).
 5. Circuit as claimed in claim 3 or 4, characterized inthat the sense semiconductor circuit elements are integrated on onejoint semiconductor material (9), and one joint selectable referenceelement (R_(S)*), in particular a reference resistor, which is notintegrated on the semiconductor material is provided for currentdetermination.
 6. Circuit as claimed in claim 5, characterized in thatFor current measurement the voltage drop across the reference element(R_(S)*) is determined, and each semiconductor circuit element in turncan be connected so as to be conductive to the reference element bymeans of a connecting circuit (10 . . . 13).
 7. Circuit as claimed in atleast one of claims 3 to 6, characterized in that at least two loads (3,3′) are driven by respectively one driver associated with the load, andeach driver includes at least one sense semiconductor circuit elementwhose sense current section (8) is connectable by way of a selectingport (10).
 8. Circuit as claimed in at least one of claims 3 to 7,characterized in that the semiconductor circuit elements (1, 1′) areconnected to a joint output (15) so as to be conductive in such a mannerthat, upon failure of one semiconductor circuit element (1′), theoperable semiconductor circuit element (1′) will take over the switchingfunction of the failing semiconductor circuit element (1).
 9. Use of thecircuit as claimed in claims 3 to 8 in electronic brake force or drivingdynamics controllers for motor vehicles.